Method of making an abrasive tool



Jan. 21, 1958 G. F. KEELERlc METHOD oF MAKING AN ARAsIvE Toor.

9 Sheets-Sheet l Filed Nov. 25, 1953 .0000000900. a 0ooQoO000.

Jan- 21, 1958 G. F. KEELx-:R'lc: 2,82Q,746

METHOD OF MAKING AN ABRASIVE TOOL Filed NOV. 25, 1953 9 Sheets-Sheet 2 Jah.. 21, 1958 G, F, KEELERlC 2,820,746

METHOD OFl MAKING AN ABRASIVE TOOL Y Filed Nov. 25, 1955 n `9 sheets-sheet s a b o traba 56 J. v ,I

Jan. 21, 1958 G. F. KEELERic 2,820,746

METHOD oF MAKING AN ABRAsIvE Toor.

Filed Nov. 25, 1953 9 Sheets-Sheet 5 Jmmfmx l m @mw Worm.

Jan. 21, 1958 G. F. KEELx-:Rlc 2,829,746

METHOD OF MAKING AN ABRASIVE TOOL Filed Nov. 25, 1953 9 sheets-sheet e Jan. 21, 1958 G. F. KEELERIC METHOD oF MAKING AN ABRAsIvE Toor.

9 Sheets-Sheet 7 Filed Nov. 25. 1953 Jan. 21, 1958 G. F. KEELERIC I 2,820,745

METHOD OF MAKING AN ABRASIVE TOOL Filed Nov. 25, 1955 l 9 Sheets-Sheet 9 /ffg 20,

United States r1`his invention relates to abrasive tools' andmethods of ymaking them.

This application is a.continuation'inpart of' my prior application, Serial'No.l 357,483, ledl May '26, 1953.

A part of the invention resides in the discovery'gthat determinate arrangementsorpatterns of labrasive particles in an abrasiveitool willproduce improved-results; Such improved resultsmay appear in faster removal rates,

better and moreV uniforml iinish, longentool life, better:

clearing ofchips ordetritus, the ability to limpart a determinate cutting pattern'on the Work or intcombinations oftheseresults.y Dierent patterns'may be selected for different" kinds ofI applications.`

Accordingly,`one of theobjects of-ithisjinvention isjto producel any abrasive tool* of determinate ypatternV or ar-` rangement of the abrasive particlesin it.

Another objectisv toprovide a' method of making abrasive tools by which a wide-range ofideterminate'panl ticle arrangementsmay'be Iobtained at reasonable cost and as-a practical productionV technique;

Another objectisto Vprovide an abrasive-f tool in whichv the'number of abrasiveparticles is greaterwherever greatest wear isf normallyfencountered, as; forlexamplegto'- ward any'edge'of theI tool' over'which Aa-workpiecenor-r mally enters or Vleaves the-working-areaof thevtool.`

Another vobject is to provide anabrasive-tool1 in: whichA abrasive particles'areVV held rin place by=va combination off resin or plastic bond and metal bond.

A related objectlisfto-provide Va method of 'making `aninexpensive, single-*layer abrasive tool.-

Other objects will appear-'in Vthe description ofthe rinvention which follows.

in the drawings:

Fig, 1 isa front elevation of part v=of an abrasive-tool-I made accordingv toythis invention. (Dierent portions of the drawing show meansffor achieving diferent densi- ,3

ties ofV abrasive `particles inthe finished 'tool.)

Fig. 2 shows a sideelevaticn ofa iinishedabrasive tool of the peripheral-working-surface type` made according to this invention.

Fig. 3 is aperspectivesview.v showingahoningntool Figs.v 9 tol4; inclusive, showtsteps in another mode -of manufacture ofabrasive tools according: to.v t this inven-f tion; Each isthessame: fragmentary sectional-view exs.. cept that Figs. 9, landsllzaref-partly `in elevation;

Figs- 15, 16.- and117 show steps in atvariantmethod off manutacturingy abrasiveetoolsfaccording:tazthis-imtentimnv Figs.; 1.6...andil17 are partly:"inrsectiont- Fig; 1S -is :asectional .'vie'svaof apparatuszusedriinian als.

I 2,820,746 Patented Jan. 21, g

ternative: methodof making abrasive tools according` to this invention.

Fig. 19 is'a partially retouched,photograph oa screen used in'the apparatus of Fig. 1S.`

Fig. 20'is a partiallyretouched photograph of'a pair ofscreenslike thatl oFFi'gei i9`mounted together to form a cross pattern.

Referring to Fig. l; thereis`shown a" metal` backing plate 2 having avhnb portionjand a set-screw 6 for fas.- tening it to ai grinding spindle.

Onthe backingjplate'Z; as shown', thereare" abrasive' elementsS'I arrangedin'a" geometric pattern: These elements .mayf consist' of' single vabrasive grains' or particles, such'asfdiamond borts', orl they may -'consist of'clusters of smaller particles, as shown iii-more detail inFig.' 6 or' Fig;.14.' The elements fmay b'e round, as' shown, or they may ibeofany :desired shape, inciuding curvilinear shapes extending;alliacrossltheworldng'surface oflthe tool.

The*determinatiomofthe patternor arrangement of the elementsfwillldepend ona number of factors.

Oneof these'iis finish.v lff asmooth finish is desired,

then the pattern as 4it passes `over theworli`l shouldnotV produce'scorelines,and, collectively, all 4the elements 8 shouldnotr fall one directtyfbehind'the other (in the sense :of rotation), but :'should.l beso arranged that each cluster is :alittle-'displaced from the-one preceding it so thatfthepathfoffeach'element overlapsl the path of another. Thisfmay bet'betterfunderstood'by considering vthat inforderto.producepa".linedfsatin finish the elements will be. arranged'V so :thatU the 1 overlapping is deliberatelyV minimized.

Another important f.consideration-is'cntting speed.y Itf is known that im. atv conventional',K randomly' oriented' is, ifaworkpiecali squarefinsectiort is pushedagainst a moving 2.grindingw-heel withfa forceiof, say lOJpoun'ds," it 'may` be` ground zaway. ata-.-rate:of,\1 perhaps; 1/16 per minute. But ifa workpiece l" squareV ispushed 'against the same moving grinding wheel even with a force 16v times as great (because.itssectionalareais 16 times as great), it ,will notbe ground away-at-.the samerate ofl per minute butV at. some lesser rate.

Theories have been propoundedn to explain this phenomenon. One'surmise is that, as any abrasive grainv or particle advances across a large workpiece, it gathers ahead of 'itself some ofthe material it has removed, and, if thismaterial Iis notwashedaway or disposed of, it will4 reduceI the abrasive e'ectiveness of that grain during the latter part of-its passage across a large Workpiece. ln .a random arrangement 'of parti'cles, someV of` them may be grouped'together'to trap the removed materlal or, at best, to oer-'atortuous and `uncertain path for escape..V Thissurmisetis. partially supportedby the' fact that a workpiecewhich isrectangular insection will be ground more rapidly. (withwequal grindingpressure) v when it is held with its long axis perpendicular to the direction of motion of the grindingwheel than when the' as large `.as fthe nelements themselves; and that the open channelstlead inadirectionapproximatelyin a` general waylthefreepathlwhich ya: drop oflliquidtakes as the composite resultothemotionlof the wheel-onother tool and the holding eiect of the workpiece and other frictional factors.

Another useful factor is to shape the abrasive elements themselves in such a way .that they tend to plow the detritus to one side (or both sides) instead of piling it up against a frontal` edge. Thus, if square-shaped elements are used, all of them should be disposed so that corners of the. squares rather than sides advance toward the Work. Round, diamond-shaped, triangular or hexagonal elements may also be used satisfactorily. Indeed, it is not the shape but the inclination of the advancing edge away from perpendicular to the line of advance to give a shearing action which is important. yWhere the motion of the tool is rotaryand where the working surface is frontal rather than peripheral, then it is desirable that therangle of the advancing edge should tend to throw at least a portion of the detritus outwardly in the same direction as the centrifugal force tends.

Where the abrasive tool is to be used in electrolytic grinding, as disclosed, for example, in my co-pending application,Serial No. 310,244, led SeptemberlS, 1952, forfMethod and Apparatus for Electrolytic Cutting. Shapingand Grinding, another consideration is to provide an easy flow for electrolyte, and for this purpose cross paths may also be helpful.

Another important consideration in selection of pattern of arrangement is that the number of elements should be greatest where the wear is greatest. Thus, in a grinding Wheel'as shown in Fig.. 1, the greatest number of particles should be located near the outer limits of the annular area constituting the. Working surface of the wheel. This is where greatestA wear occurs due to highest velocity. When the workpiece travels (relatively to the wheel) all the way off both inner and outer limits of the Working surface at each pass, with an advance toward the wheel with each pass, then there should be 4an increased number of elements both toward the inner and outer limits of the working area.

The geometric pattern shown in Fig. 1 meetsV manv of these considerations in a favorable manner, although other patterns will also do so, and although for different kinds of Work different patterns will be chosen to emphasize some one or two factors even at the expense of others. i

. In Fig. 1, the grinding wheel shown by way of example has a diameter of 13 inches. The working surface extends inwardly 21/ inches, so that its inner diameter is 8 inches. The abrasive elements 8 are round and have a here, it is intended that each abrasive element consist of a plurality of abrasive particles, as shown in Figs. 6 and 14. Where the elements are of the order of 1,66 inch in diameter, as in Fig. l, there may be as many as eight or ten 4or even more abrasive particles in each element, depending on the grit size used. In some cases, however, the elements 3 may be small, and'only one grain will be used in each element. For example, the elements may be .014 inch in diameter and with particles of grit size from 60 to 80 then only one particle will be present in each element.

The abrasive elements 8 are disposed in a geometric attern arrived at in the following way. A circle of centers c-c-c having a radius of 3 inches is drawn from e center :of the wheel. VThe circle of centers is then divided into an integral or whole number of parts to lstablish centers for the pattern circles designated p-c. ese centers are spaced about '/52 of an inch apart. utwhat is important is rthat the divisions be uniform all l ound the circle of centers, Thus, the distance between ing off with dividers),'so that even divisions occur.

The pattern circles p-c intersect at` numerous points, ud. all the pointswithin the working area serve as centers diameter of a little less than TA6 inch. In the form shown enters may be adjusted slightly as necessary (as by step- A for the abrasive elements 8. This is represented in sector marked a of Fig. l. N

If additional coverage is desired, then the number of elements may be doubled, as illustrated in sector b. Additional pattern circles are drawn from centers on the circle of centers c-c-c, which are mid-way between the centers used for the pattern inL sector a. Since each pattern circle intercepts `theworking area twice, the result is to quadruple the number of intersections, but only half of this quadrupled number is used in sector b as abrasive elements 8 are placed only on alternate intersections ofthe ingoing cycle of each circle (taken always in the same sense).

In sector c all vofV the intersections 'of all of the pattern circles are used, so that in this sector there are twice as many elements per unit area as in sector b and four times as many as in sector a.

It should-be understood that each sector represents a possible pattern to be carried over the entire workings* surface of any given Wheel, and that the showing of the First it will be observed that, viewed inthe direction of rotation of the wheeL'any given point on a workpiece will be traversed by as many elements regardless of whether the workpiece is placed near the inner or outer limit ofthe working area. This result could be obtained, of course, by a pattern'formed by the intersections of evenly' spaced radii with a number of evenly spaced concentric-circles. However, the higher speed of the elements v near the periphery would cause more wear on them. Thus,

it would be preferable to bring the concentric `circles closer together as they approached `the periphery in order to oiset this tendencyto wear. While such a pattern would Y be quite satisfactory over a narrow-band working area, the result in anormal-Width working area would be to open up near the periphery a` considerable space between elements viewed in the direction of rotation and, at they same time, to close up the space between elements viewedV radially. Thus, the larger area near the periphery would. be used less effectively than optimum. Or if it is used with an optimum arrangement, then the inner area would be less well used.

Referring backto Fig. 1, it will be seen that while any point on a workpiece will be'traversed by the same number ojf elements,- the actual number of elements near the periphery is much greater than the number'at the `middle or inner portion of working area. This isv because of thel pattern of intersections. It will be observed,also, that the density of elements (as distinguished from the number) is greater near the inner and outer edgesl ofl the working surface, thus resisting wear at these points.

Here it should be pointed out that the principle of the pattern isnot` confined to greater density near the'inner and outer edges of a working area, but is directed to using greater concentration wherever greatest Wear occurs. Thus, if the working surface of the'wheel is not flat, as in the wheel of Fig. 1, but if it is contoured upwardly at some mid-portion for form grinding, then a pattern will be selected to put a greater density on the high area, for in such a situation the workpiece will be advanced frontally and will cause more wear on the high point.

So much for the distribution of elements with regard to wear.

are formed and thatthey follow approximately the path which is taken by a drop of liquid introduced onto the This I have determined by experiment.

moving wheel. Since grinding wheels are customarilynsed witlrcoolant,

electrolyte, or other liquid, these .channels serve toV fa-v Itwill be observed also, particularly in sector l b of Fig. 1, that open channels for removal of detritus` e exactly .the path the ,liquid would naturally take' (which inanyA case willvary withits mode, direction and velocity of application), but that re'atively unobstructed channels be open to the fluid in its generally outward travel. Thus, a pattern of elements closely spaced in concentric circles solthat little lflow between the elements is possible will `be undesirable.

It isalso desirable to provide. cross channels toragitate the uid,'to produce turbulence and to assistl in carrying away `the detritus without pile-up. This is particularly desirable where ythe wheel is-to ibe used in electrolytic grinding. Vit will be observed that the channelsdefined by the'contiguous spaces between the elements constitute two sets of crossfehannels, one Aset following the liquiddrop Apath Aresulting from one direction of rotation, and the other following that resulting from opposite rotation. The cross channels can` be observed most readily by Aholdingthe lower, right-hand corner of the drawing close to the eye .withvthe drawing nearly parallel to the line ofl sight. Por sector b the larger open channels follow the liquid-.drop path resulting vfrom rotation in the directionof the arrow.

Fig. 2 illustrates a simple form of peripheral grinding wheel havingva plate section 2 and a hub 4 by which it is mounted on ,shaft The abrasive elements S are diamond-shaped. While the drawing shows the diamondshaped elements as quite large, it will ordinarily be preferable `to use a dimension lin the long axis of the order of .015 inch and in the short axis of the order of .006 inch. Whatever the dimensions used, the width of the channels between elements 8 should be lnot less than the.

small dimension of the elements themselves and, preferably, at lleast as great las the large dimension of the elements.

Fig. 3 is a perspective View of a honing tool. The body 3 2 Vcarries a metal bond 3d in which are imbedded abrasive particles 36, which are preferably individual grains, each of which protrudes a determinate distance above the metal bond 3.4.

rldig. 3-A is a fragmentary sectional view along the plane 3a-3a of `Fig. 3. The particles 36 are preferably diamond borts and, as here shown, are intended to protrude .993 inch above the metal bond 34.

The pattern of particles is a rectilinear one, but itis intended Athat the hone be used inside a cylindrical surface and moved longitudinally of the cylinder while rotated relative yto it, thus following a generally helical path. The particles 36 serve to score the cylinder wall with score marks nearly .063 inch deep. The hone may then be operated with the longitudinal motion reversed as respects the rotary motion, thus producing -a cross pattern of ne score marks of determinate depth, spacing and pattern. This will be useful in the treatment of cylinder walls .which have been plated with chromium or other hard material in establishing a fine network of score marks to aid in lubrication. The treatment of cylinder walls in this way is no part of this invention, which is conned to abrasive tools (including the honing tool) and means of making them.

Any Vof the abrasive tools above described may-be made by hand, placing each abrasive particle in its appropriate position inthe desired pattern into a matrix or bond, which is soft at the time of placement and susceptible of being hardened thereafter. Such a procedure may be satisfactory for the making of one or two abrasive tools for some special application, particularly if the tools are quite small. But if the patterned abrasive tool is of the size used in many industrial applications and if more than one or two are to be made, then it will bedesirable to provide more rapid production techniques for making such tools.

In Figs. 4, 5 and 6 and Figs. 9 to i4, inclusive, steps irl-methods for rapid production of s uch tools are shown. The gistof the method is the formation of apatternof adhesive imprinted in such a way as .to hold abrasive particles .in thedesired. coniiguration until V-a heavierI `and stronger bond of metal may be built around the particles.

`Referring to Fig.4, .a sect-ionrof a backing wheel 2 is shown. Uponthe-workingsurface of the backing wheel are printedfthe elementsa ora desired pattern. These elementsfare printed in adhesive of a kind susceptible of` being heatcured at a later step in the process, so as to aid in the rformation of a suitable bond for holding the particles in position.

The placementof thel pattern of adhesive may be carried out in several ways. t may, of course,be done by hand, butit is preferred to establish the pattern on Ya rubber ystamp, which will haveon it all ofthe elements f'the pattern, which ywill then be covered lightly with theradhesive andpressed against backing plate Z, thereby leaving very-thin ,layers of activated plastic adhesive .at the-points where-each abrasive-element is tobe located.

The rubber-stamp technique is desirable because the desiredpattern may be drawn with :pen and ink `(as shown,

for example, -.in Pig. l hereof). The pattern thus producedbypen and ink may be reproduced in a rubber stamp by any of the-.several available photoengraving techniques which-are used inmaking rubber stamps bear ing signatures or other patterns for a multitude of uses.

ln'imprinting-the pattern with the rubber stamp, precaution rnust be taken that the stamp is located accurately on the backingplate and that the rubber stamp is not pressed toohard, for if it is, the pattern elements in the stamp may spread in an uneven and undesired way.

While the rubber-stamp technique will be desirable for complicated patterns, it is also possible to achieve the desired result in simpler patterns (e. g., as in Fig. 2,) by use of a knurled roll, which may be of brass and which can be used toimprint the pattern shown in Fig. 2 hereof on the periphery of the grinding wheel shown there. Where the knurled roll isused, it will be desirable to provide continuous feeding means so that uniform thickness of adhesive will be imprinted onto the backing plate.

As adhesive, a number ofmaterials may be used satisfactorily. .Good resultshave been obtained with-a material known as Alradite, produced by Ciba andvCompany. This material is one of the ethoxylenes, which are condensed products of polyarylithylene oxide compounds with acids and hydrates, amines and other compounds. The advantage. of. this type of material is that during curing it produces little or no water or other volatile material.

The plastic adhesive should be applied quite thin for easy printingof the pattern, and, if the above-identified plastic is used for this purpose, it will be diluted with toluol.

After the plastic adhesive pattern has been imprinted on the backing plate, it is allowed to dry, so that some of the solvent passes olf. This process maybe accelerated by heating, but the heating should not proceed far enough as to cause permanent hardening or curing of the plastic.

After the adhesive has dried sufficiently to become tacky, Vdiamond bort or other abrasive particles l@ are spread over the patterned surface, with the result that particles will adhere to the portions where the adhesive.

pattern has beenimprinted, as shown in Fig. 5. if the elements of the pattern are large with respect to the particle size, then a number of particles will adhere to each element. But if the particles are large enough with respect to the size of the elements, then only one particle will adhere to each element. Thus, for example, if the element is circularin shape and has a diameter of .0l 4 inch, Vand if the abrasive'particles are of 6G to .SG grit size, ithen therewill be room for only one grain on each dot vor element.

After the particles have been spread in an excessive qn-antityfacross thesurface to cover it, giving opportunity for `the-particles to adhere Vto the adhesive, then the remainder of the ,particles are .brushed or .blown 0E.

At this stage the .sectional view of Fig. 5 indicates the ments 8a. 'l

l," YThereupon, the surface of the backing plate 2 is pre- ;pared for electroplating.V If heat has been used to drive off thevolatile solvent fromfthe adhesive, then it vmay be inecessary to pickle the surface of the backing plate 2 in iorder to free it of oxidesfor scale. When this has beenV ldone, the entire backing plate 2, with the adhesive ,elements 3a and the abrasive particles 19 in position, is elec- 'troplatedv Usually, it will be desirable to mask the nonworking surfaces of the backing plate in order that elecarea. Referring to Fig. 6,' the metal deposit 12 Amay be copper, nickel, iron or a combination of these may be iused for goodadherence and the desired degree ofrrm- `ness in holding the abrasive particles. The electrodeposi- ,tion will be carried forward until somewhat more than half of the depth of the abrasive particlesis reached. :It should be noted that the adhesive Yused is thinenough, Vand its insulating qualities poor enough, so that metal is Adeposit'edright overy and through the adhesive elements l8a as well as directly to the metal of the backing plate 2. By this means, very close holding of the abra- .'sive particles 10 is obtained.-

After the plating is complete, the entire assembly is heated to a high enough temperature to set the adhesive lso that it becomes a permanent plastic having considerable strength. Thus, the plasticV aids permanently in .holding the abrasive particles in place. If desired, the

lWhich case, however, special care must be taken to clean lthe metal of scale and oxides before plating.- It will be noted that the same technique may be used rangement of abrasive elements or particles. As shown in Figs. 7 and 8, the entire surface of a backing Wheel may be coated with plastic adhesive 7 and abrasive par jiticles 14D distributed over it in any desired manner. l example, the distribution may be achieved by mixing the `particles with someV soluble or otherwise removable parlticles,` which are then vdissolved or otherwise removed, l as disclosed Vin my co-pending application, Serial No. 11,314,881, led October 15, 1952, now Patent vNo. 12,785,060, for Method of Distributing Particles and Abrasive Article.

The -same steps are then followed as have been described above in connection with the patterned tool, but in this instance all of the plating will be carried von through f the plastic adhesive. It has been found that this can be done eifectively if the plastic adhesive is very thin. After i the plating has been completed, the assembly is heated to 1 set and cure the plastic adhesive so that its bond becomes strong and permanent.

A variant of this procedure is shown in Figs. l5, 16

covered by a thin layer of plastic adhesive 9 diluted with a suitable solvent. The coating may be accomplished Q simply by Yirnmersing the particles in the plastic or it may tbe accomplished by blowing the particles through a spray .of the plastic. If desired, electrostatic'means maybe used inrthis latter procedure to maximize the impingeyment of plastic adhesive on the abrasive particles. i After the plastic adhesive 9'has been vapplied to the Iparticles 10, they are dried, preferably .with application of moderate heatV sufficient to driveV o the solvent but ,not sutlicient to set the plastic.V The result of drying is "that the particles cohere one to another to'form clusters, and yit is necessary then to run them in al ball mill in order to break up the clusters into individual particles, each coated with a thin layer of activatedplastic adhesive. vThe coated particles are shown in Fig. 15.

'The particles are then distributed overfthe surface of nbacking plate 2 in anydesired manner. If desired,-the ybacking plate maybeinscribed with grooves to establish a desired pattern `into which the particles willjfall. The

`trodeposition of metal may be confined to the workingV ,curing maybe carried out prior to the electroplating, in

for making abrasive tools without having a patterned at-,

and 17. The abrasive particles 10 areiirst completely :abrasive particles IO'adheringto plastic'adhesive ele'.v

For,

entirefbacking'plate `2, togetherl with the adhesi`vicfoatecii n particles 10, is then heated'.- As this is done, ,theplastici adhesive will lirst soften'and become tacky and adherent, and will then set and curev as a hard and strong material l This stageis shown in Fig. 16.

The metal surface of the vbacking plateZ isthfenclevaned to remove oxides or scale, and then, as shown'in'Fig;VV 1 17, metal 12 ,isv deposited electrolytically to surround n and hold the labrasive particles. Y By this means, the'ab'rasive particles or grains are held both by a plastic envelope47V around each particle and a metal 'bond outside'the plastic p envelope. VThe plastic is somewhat-softer than the-metal,`

and for some kindsfof service this is advantageousiin that shock against the particles, which tends tobreak or crush Vthem or loosen themfrom their bond, is `cush-V ioned slightly by the plastic envelope.

irst softens and ilows slightly before hardening.

The general method thus described, characterized-b the use of both plastic-and metal bond, `constitutesa way of making either a patternedv or a randomly oriented For many applications, -such an abrasive tool will be entirely satisfactory, but'gfor some 'applications it will be desirable to control moreabrasive tool at low cost.

accurately thefamount of protrusion `of the abrasive grains or particles above the bond vthan is achieved in -the method previously described, for in that method,'since the grains will not be identical in size, it follows that the larger grains will protrude -somewhat higher thanthe If it is desired to assure that the nuten;k most points orsurfaces ofthe grains lie in one planta. which maybe desirable, for example, in electrolyticl grinding as disclosed in my c'o-pending application, SerialV smaller ones.

No. 310,244, tiled September 18, 1952, for Method and Apparatus for Electrolytic Cutting, Shaping and Grind'-y ing, then the method shown Vin Figs. 9 to 14, inclusive,

should be employed. 1 f Y The method about to' be described constitutes'an advance over the methoddisclosed in my Patent-No;

2,368,473, issued .T anuary 30, '19475, for Method kof Mak` ing Abrasive Articles. Here' again, thef cruxY of-the method is the initial imprinting of the desired` pattern of elements with an adhesiveto hold the abrasive par-Y ticles or grains in the desired arrangement. However, q as indicated in Fig. 9,-theV adhesive elements 8a are .not j imprinted on a backing plate but on abla/nk 3, lwhich may be at or contoured, as desired. The blankv 31is used in the process of manufacture but forms no perina'` nent part of the abrasive tool. `V'lfhe adhesive elements Sa are imprinted onto the'blank by any of the techniques f heretofore described. The adhesive layer should bevery thin, so thin indeed that it -has 'not -been'ipossible to measure it by any ordinary mechanical measuringtechnique.

The abrasive particles710 are then vscattered over lthef surface of the blank so that'they adherey tothe adhesive4 Ordinarily, no elfo-rt will 'be made-to sep-.v arate oridistribute the particles 10.,over the surfacelof the elements 8a, but, if desiredthe abrasive particles' may be mixed with salt, as disclosed: in my co-pending` application, Serial No. 314, 881, led October 15,*11952,V for Method of Distributing Particles i and Abrasive .,Article.

Or, if desired, the elements 8a may be small enough Vso v that each will hold only,one abrasivegrain o'rparticle t 10. In any case, only one layer of particles 10. will ad-; here to eachelement 8a. YThis is assured Ybyh'oldirrg'tht; f thickness ofthe adhesive to a very smalldimension,

elements 8a.

ase-e746 The excess particles are brushed E or otherwise ref moved from the blank. This stage is shown in Fig. 10. Thereupon metal 12 is elecrolytically deposited on the blank 3, some of it being deposited through the adhesive so that a close and tight bond is achieved around the particles and through the interstices between them, as shown in Fig. 11. The initial deposit of metal may be of copper 12e and will be of the same thickness as is desired ultimately to be the amount of protrusion of the particles il) in the tool. Thus, for example, in making the hone shown in Fig. 3, the metal deposited at this stage of the operation will be .003 thick.

After the initial layer of copper or similar metal has been deposited, there is then deposited a thicker layer of nickel or iron 12a to completely cover the particles 10.

Thereupon, the electrodeposited metal is all removed from the blank 3, as shown in Fig. 12, and is soldered or otherwise permanently fastened to a backing plate 2, as shown in Fig. 13. Thereupon the layer of copper 12C is etched away, leaving the abrasive particles 1@ protruding from the metal bond, as shown in Fig. 14.

lt should be noted that the blank 3 should have a surface to which the electrodeposited material will not easily adhere, so that the separation can be easily accomplished. There are many ways of bringing this about. One easy way is to use a very thin lm of oil, wax or graphite on the blank before beginning any other operation on it. The film should be so thin that it will offer little or no resistance to the pasage of current for electroplating but will still prevent a formation of a solid or permanent bond between the electroplated material and the blank. it should also be noted that, if desired, the backing plate 2 may be afhxed to the electrodeposited nickel or iron 12u prior to removing the electrodeposited material from the blank 3. When the electrodeposited material is to be a'ixed to the backing plate 2, it will usually be necessary rst to grind the back surface of the electrodeposited material in order to have it smooth and even.

A preferred method of forming a desired pattern is illustrated in Figs. 18 to 20, inclusive.

In general, this method consists in making a screen or stencil through which abrasive particles are deposited on an adhesive-coated surface of an electroplating blank or of a grinding tool itself. Ordinarily, it is kpreferable to bring about this deposition by electrostatic means.

Referring to Fig. 18, a blank 3 in the form of a ring is first coated with a very thin layer of adhesive 3. This covers the entire working surface, no effort being made to establish a pattern at this stage. This is done before the blank 3 is assembled into the complete apparatus of Fig. 18. The blank 3 is then mounted in a. mounting ring 41, which is made of an insulating material such as Lucite. The blank 3 fits closely but not tightly in mounting ring 41 and is clamped by thumb screw 43. The lower surfaces of blank 3 and mounting ring 41 (as shown in Fig. 18) should be flush, and thumb screw 43 will be tightened when this relationship is achieved.

This assembly of blank 3 and mounting ring il is also carried out before they are mounted in the complete apparatus of Fig. 18.

This apparatus provides an insulating frame for holding abrasive particles lil, pattern screens d5 and 45a, and blank 3 in proper relationship to permit electrostatic deposition of the particles on blank 3.

An annular base member i7 of insulating material is recessed to provide a receptacle for an annular metal tray i9 in which the particles 1li are placed. The tray 49 may be trough-like in section or, as shown, it may have a number of recesses S1 drilled into it. The advantage of the recesses is that they form a number of pockets which may be readily filled by dusting the abrasive powder through a sieve and may then be leveled oliE by wiping the `excess .powder away, Diamond powder of grit size from 200 to 400 mesh has proven very satisfactory. indeed, one of the surprising aspects of the invention is that this relatively fine abrasive yields cutting speeds more like those normally expected only with much coarser grains while, at the same time, giving a fine finish in a single operation. to mesh may also be used, but the invention is concerned with using abrasive powders rather than with using individual cutting stones susceptible of being practically handled piece by piece;

it is desirable in many instances to mix the abrasive particles id with another powder of soluble material, such as sodium sulphate, so that initial spacing between the abrasive particles will be brought about. At a later stage in the process, the salt `is dissolved away, thus bringing about a separation of the abrasive particles. The use of the salt-dissolution method is fully disclosed in my co-pending application, Serial No. 314,881, filed October 15, 1952, for Method of Distributing Particles and Abrasive Article.

lt is preferred to make the mixture of about 35% diamond powder and about 65% soluble salt, so that when the salt is dissolved away, the diamond density is about 1/3 what it would be if no salt were used. The patterns used preferably result in open spaces on the grinding tool of 1/2 or more of the total area. Since each abrasive element of the pattern contains only 1/sL the maximum possible amount of diamond powder, it follows that the tool as a whole has only s or less of the maximum possible number of diamond particles. This appears to be of great advantage in increasing the cutting speed and, indeed, a total coverage even less than this (for example, that obtained with the cross pattern illustrated in Fig. 20) gives higher cutting speed.

A fixed center plug S3, made of insulating material and having a center bore 5S, lits closely within base member 47 and rises to a height ush with the upper surfaceV of base member 47. This surface is approximately half any inch above the surface of tray 49. This is substantially the distance the particles lil have to move under the inuence of the electrostatic eld, and this distance is satisfactory for particles from 200 to 400 grit size. lf larger particles are used, the distance may be narrowed by raising the tray 49, or the potential of the electrostatic eld may be increased.

The fixed center plug is removable for cleaning purposes but normally remains fixed within base member 47.

The tray 49 is set in place in the recess of base member 47 and is loaded with the mixture of abrasive powder (usually diamond bort and salt. A connector screw 57 threaded through base member i7 is then screwed down to make electrical Contact with tray 49, connector nuts 59 are tightened over lug connector 51 so as to make comiection to a high-tension lead 63.

Neat, pattern screens i5 and 45o: are laid across the upper surfaces of base member 47 and center plug 53.

These pattern screens are shown in Figs. 19 and 20. 19 shows screen which is made of brass of .015 thickness. The curved slots shown in white conform to the pattern prineirles previously described and are cut through the brass by engraving lathe. Screen 55a is the same as screen @5:5 except that it is made of much thinner stock, usually about .003. lt is possible to use screen 4S alone, producing a pattern conforming to the curved slots. Often, however, it will be preferable to pro-duce a pattern of smaller individual abrasive elements, and this may be done by placing screen 45o on top of screen but in the reverse sense so that its slots cross those of screen this is done, a pattern appears like that illustrated in Fig. 2Q, which is alretouched photograph taken of the two screens laid together against a light background with screenida on top and screen 45 beneath. i

As a practical matter, `it has proven desirable `to use slots the lower screen, e. g. screen 45, which arenarf Larger grit size up fand then soldering it to screen 45a.

:of damagel in handling.

source oiff of course). Y or less permanently to connector screw 57. Another lead 63a is connected by Fahnestock clip 71 to thumb screw 43. `The voltage source should provide ,about 10,090 volts and may consist of a vacuum tube rectier :system or any other suitable supply. a Once the connections aremade, the'source 1s turned tower than-those used in upper screen. 45a. This is because even when screen 45a islmade `of stock which is as thin as is practicable, there is still some diffusion of the pattern cast by Vscreen45. The result is that as the particles pass on through the slot openings in' screen 45, they spread one from another even in a very short path. The amount of spreading from the slotsin screen 45a Ethe particle-bearing abrasive elements are considerably `longer in one dimension than in the other. By using slots in screen `45 .which are approximately 1/2 as wide jas those in screen 45a, the pattern of particles cast by isjcreen 45 `will be approximately the sameV as that cast lby screen 45a, and the result will be theproduction of fa' cross-pattern of rsubstantial' symmetry.'

The relative size of slots vin the two screens will Vbe varied in accordance with the absolute size of the slots, with the thickness of screen 45a, with the distance of screen 45a from the adhesivelayer on the electroplating Ablank, and, of course, with the nature of the pattern jdesired. Assuming that a symmetrical pattern is desired, fthe wider the slot openings the less relative difference in their Vwidth there will need to be. The thinner screen `45a is, the more nearly alike the slots in the two screens may be. Similarly, the farther the adhesive layer is from screen 45a, the more nearly equal the slot open- .ings in the two screens may be (although if there is any :substantial distance between screen 45a and the adhesive layer, the pattern `will be so diffused as'to be unsatisfactory). Y

VIf desired, the two pattern screens 45 and 45a maybe permanently fastened together; for example, by tinning one ksurface of screen 45 with a very thin coat of solder In this way, each screen supports the other and minimizes the likelihood When the two screens are placed on the base member V'547,"screen 45a made of the thinner stock will be placed `ontop toward blank 3 so that there will be a minimum distance between screen 45 and blank 3. Unless this is done; that is, if screen 45a is too thick; the pattern :cast by screen 45 on the blank 3 will be diffused and not ,Y sharp.

When plating blank 3 in its mounting ring 41 is placed.

above screens 45 and 45a, spacing shims 65 are placed between the upper surface of base member 47 and the Y Hlower surface of mounting ring 41. These shims may.

be of paper or of metal shim stock and have a thickness :of about .002. Their purpose is to space the adhesivejbearing surface of blank 3 away from screen 45a so that ithe adhesivewill not be transferred to the screen.

Finally, movable centering plug 67, also of insulating material, is zplaced by metal handle 69 into the assembly. IThe plug proper lits tightly on handle 69 and the lower fportion ofthe handle passes through center holes of ,screens 45 and 45a, and thence into` bore 55 of center plug/53. lare centered and brought into proper lateral relationship.

By this means, all of the working components A high Voltage source is now connected (withy the The lead 63 is connected more on momentarily. The particles will thus jump `upwardly, and some will pass through the openings in patn tern screens 45 and 45a and onto the adhesive on blank' being closer tothe adhesive is considerably less, so thatV It is also possible, of course, toY cut the desired pattern of openings into a single screen.V vOther desired patterns may be producedv in this way to 4 give substantially any pattern arrangement which may be desired. Thus, circular openings may be cut into the (screen in pattern arrangements like those shown in Fig. l. yOr otherdesign patterns may be provided in similar ways.

assunse 3,.where `they will be held. Inthis way the particles will be placed on the yblank in a pattern determined bythe screens. i Y

The effectv of the electrostatic deposition is to orient the particles so that their long axes are normal to 'the` plane of the working surface of blank 3. Abrasive Vparticles, such as diamond bort, are ordinarily irregular in shape, and the long axis refers to whatever dimension across the particle is the longest. With most diamond.

particles the crystalline structure isV such that the longer and shorter dimensions are readily seen in a microscope.V

In any situation where the Vorientation of the particles is not important, it will be possiblek to deposit the particles through the screens onto the blank by placing theV blank with its working face up, then placing the lscreens v over the blank, and then sifting'abrasive powderonto the blank through the screens.

After the particles 10 have been deposited, as def" scribed, on the adhesive 8 of plating blank 3, the blank in its mounting ring 41 is removed from the apparatus and the blank is then taken from the mounting rin.

The adhesive is allowed to set and the blank is then immersed in water to dissolve away the salt particles; 'Atv y this time, there will be on the working surface of platingV -blank 3 a plurality of abrasive elements, each consisting of a number of abrasive' particles, each particle separated slightly from the next by the spacesfformerly occupied by the salt particles.,

The non-working surfaces `of the blank are then covered or masked with insulating plastic material. This may be done by'immersing the blank ina hot plastic material while keeping the workingsurfacecovered. The plastic adheres to the blank and prevents the deposition of metal except on the working surface in the plating stepswhich'follow The blank `Ilis then immersed in anV electroplating bath to deposit a thin layer of copper, and then in another bath to deposit a heavier layer of nickel or similar material. The ring of electrodeposited metal is then stripped away from the blank and carries` the abrasive particles in it. The blank is stripped of the plastic material and is cleaned, and is then ready for use again. The copper deposit is then chemically removed from the nickel or other material, leaving the abrasive particles protruding by the thickness of the removedcopper layer, and leaving the extremities of the particles all v in substantially the same plane. This part of theprocess4 is disclosed in my prior Patent No. 2,368,473, issuedl January 3f), `1945, .for Method of Making vAbrasive Articles.

The grinding tools made in accordance with this in'- vention in which diamond particles are arranged in a desirable cutting pattern in low density of coverage and are'Y because'fewer diamond rparticles are used due Yto thefact` that so large a portion of the total working areakis yleft open. It is believed that some of the increase in cutting speed may arise from the very factthat fewer diamond particles are used, with the result that there is a higher unit pressure of the workpiece against all of them. It isr very difficult or impossible, however, to achieve this result if the elort is made to distribute an equally small number of particles purely at random, for when the total number of particles is small, the likelihood of great unevenness in random distribution becomesy quite serious, Y

and prevents achievement of an optimum result. y

f The method disclosed herein which pattern screens/are used permitsfa wide variation in pattern design. llt per'- assume 13 tion of large numbers of grinding tools and it assures that the pattern is uniform throughout each tool and from one tool to the next.

There is one other aspect of the use of a pattern in an abrasive tool which is quite unrelated to utility. There are some applications for abrasive tools in which, Within certain broad limits, the pattern is not of any serious importance in the usability of the tool. This will be particularly so in abrasive tools used in small shops for a wide variety of purposes, and Where the utmost in economy, cutting speed, finish, etc. are not of great importance. For sale to such users, the artistic effect of the pattern may be of as great commercial importance as its direct utility, and the methods which have been described will be of considerable value in permitting the use of patterns of wide variety aimed at producing a pleasing appearance rather than at utility.

It will be seen that by this invention abrasive tools are provided having determinate arrangements of the abrasive particles in them, so that optimum utilization of the particles may be made or so that a pleasing artistic appearance may be obtained. It will be seen also that inexpensive methods of making abrasive tools, either of the patterned type or of the randomly oriented type, are disclosed and, also, that a method is disclosed for making a patterned type abrasive tool in which the advantage of uniformity in protrusion, as disclosed in my Patent No. 2,368,473, is attained.

While a preferred embodiment of this invention has been shown and described, it will be apparent that numerous modifications and variations thereof may be made without departing from underlying principles of the invention. It is therefore desired by the following claims to include within the scope of the invention all such variations and modifications by which substantially the results of this invention may be obtained through the use of substantially the same or equivalent means.

What I claim as new and desire to secure by Letters Patent is:

1. In the process of making a metal-bonded abrasive tool having a precise determinate pattern of clusters of 14 abrasive particles forming the working surface of the tool, the steps which include coating a tool blank with a thin layer of adhesive, placing a rst pattern screen having slotted openings therein in close proximity to and not more than .005 from the tool blank, placing over the rst pattern screen a second pattern screen having slotted openings arranged to cross the slotted openings of the first pattern screen thereby to establish a pattern of openings at the intersections of the slotted openings of thetwo pattern screens, then propelling abrasive particles by electrostatic means through the pattern of openings formed by the two pattern screens and onto the adhesive on the tool blank, then depositing metal onto the tool blank to surround and support the abrasive particles and then separating the tool blank away from the deposited metal and the abrasive held therein.

2. The method defined in claim 1 in which the slotted openings in the second pattern screen are made narrower than the slotted openings in the first pattern screen.

References Cited in the le of this patent UNITED STATES PATENTS 794,495 Gorton July 11, 1905 794,496 Gorton July 11, 1905 1,414,447 Tone May 2, 1922 1,988,065 Wooddell Jan. 15, 1935 2,152,077 Meston et al. Mar. 28, 1939 2,359,920 Keeleric Oct. 10, 1944 2,367,286 Keeleric Jan. 16, 1945 2,368,473 Keeleric Jan. 30, 1945 2,376,342 Carlton May 22, 1945 2,378,025 Melton et al June 12, 1945 2,386,626 Nadeau et al Oct. 9, 1945 2,457,156 Jones Dec. 28, 1948 2,463,241 Carlton Mar. l, 1949 2,548,872 Cross et al. Apr. 17, 1951 OTHER REFERENCES Phillips: Flock Finishing, Organic Finishing, October 1952, pp. 1l to 14. 

1. IN THE PROCESS OF MAKING A METAL-BONDED ABRASIVE TOOL HAVING A PRECISC DETERMINATE PATTERN OF CLUSTERS OF ABRASIVE PARTICLES FORMING THE WORKING SURFACE OF THE TOOL, THE STEPS WHICH INCLUDE COATING A TOOL BLANK WITH A THIN LAYER OF ADHESIVE, PLACING A FIRST PATTERN SCREEN HAVING SLOTTED OPENINGS THEREIN IN CLOSE PROXIMITY TO AND NOT MORE THAN .005" FROM THE TOOL BLANK, PLACING OVER THE FIRST PATTERN SCREEN A SECOND PATTERN SCREEN HAVING SLOTTED OPENINGS ARRANGED TO CROSS THE SLOTTED OPENINGS OF THE FIRST PATTERN SCREEN THEREBY TO ESTABLISH A PATTERN OF OPENINGS AT THE INTERSECTIONS OF THE SLOTTED OPENINGS OF THE TWO PATTERN SCREENS, THEN PROPELLING ABRASIVE PARTICLES BY ELECTROSTATIC MEANS THROUGH THE PATTERN OF OPENINGS FORMED BY THE TWO PATTERN SCREENS AND ONTO THE ADHESIVE ON THE TOOL BLANK, THEN DEPOSITING METAL ONTO THE TOOL BLANK TO SURROUND AND SUPPORT THE ABRASIVE PARTICLES AND THEN SEPARATING THE TOOL BLANK AWAY FROM THE DEPOSITED METAL AND THE ABRASIVE HELD THEREIN. 